I read that you should rehydrate dry yeast. Fine, I get that. The manufacturer says to use 100F water for the hydration period. Great. It then says to drop the temp of the rehydrated yeast to within pitching temp. That means I have to drop the temperature 50 degrees to 50F? Talk about temperature shock. I have 30 minutes to do this. Seems to me a tall order. How to you guys do this without shocking the yeast?

I hydrate lager yeast cooler than 100 F, more like 85 F. I also pitch it closer to 55-60 F and then immediately chill the fermenter to ~50 F. So that cuts the temp change required about in half.

__________________Early brewers were primarily women, mostly because it was deemed a woman's job. Mesopotamian men, of some 3,800 years ago, were obviously complete assclowns and had yet to realize the pleasure of brewing beer.- Beer Advocate

Yeah, I think 100°F is a bit high too. Fermentis (Saflager) calls for ~73°F.

I would just prepare the yeast a little earlier... no harm in that. I sometimes put my rehydrated yeast into the refrigerator to help it along. I don't think that shocks it. IIRC, you want to avoid a temp. difference of no more than ~10°F.

I sometimes put my rehydrated yeast into the refrigerator to help it along.

I didn't mention it but I do this too. I pour the yeast packet(s) into the warm water and let it sit at room temp for 15 minutes, then stir and place it in the fridge. Then I stir it every 5 minutes (ALWAYS setting a timer ). I have a sanitized Thermopen-type themometer in the slurry the whole time (it's also what I use to stir the slurry).

I didn't know Fermentis called for 73 F, I knew it was cooler for lager yeast and cooler than Danstar recommends but wasn't aware it was that cool. I'll prob hydrate even cooler than 85-ish now.

__________________Early brewers were primarily women, mostly because it was deemed a woman's job. Mesopotamian men, of some 3,800 years ago, were obviously complete assclowns and had yet to realize the pleasure of brewing beer.- Beer Advocate